Displaying similar documents to “On an algorithm to decide whether a free group is a free factor of another”

A test-set for -power-free binary morphisms

F. Wlazinski (2010)

RAIRO - Theoretical Informatics and Applications

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A morphism is -power-free if and only if is -power-free whenever is a -power-free word. A morphism is -power-free up to if and only if is -power-free whenever is a -power-free word of length at most . Given an integer ≥ 2, we prove that a binary morphism is -power-free if and only if it is -power-free up to . This bound becomes linear for primitive morphisms: a binary primitive morphism is -power-free if and only if it is -power-free up to ...

Equations on partial words

Francine Blanchet-Sadri, D. Dakota Blair, Rebeca V. Lewis (2007)

RAIRO - Theoretical Informatics and Applications

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It is well-known that some of the most basic properties of words, like the commutativity () and the conjugacy (), can be expressed as solutions of word equations. An important problem is to decide whether or not a given equation on words has a solution. For instance, the equation has only periodic solutions in a free monoid, that is, if holds with integers , then there exists a word such that are powers of . This result, which received a lot of attention, was first proved by Lyndon...

Some results on complexity of μ-calculus evaluation in the black-box model

Paweł Parys (2013)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

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We consider -calculus formulas in a normal form: after a prefix of fixed-point quantifiers follows a quantifier-free expression. We are interested in the problem of evaluating (model checking) such formulas in a powerset lattice. We assume that the quantifier-free part of the expression can be any monotone function given by a black-box – we may only ask for its value for given arguments. As a first result we prove that when the lattice is fixed, the problem becomes polynomial (the assumption...

Computing -Free NFA from Regular Expressions in ( log()) Time

Christian Hagenah, Anca Muscholl (2010)

RAIRO - Theoretical Informatics and Applications

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The standard procedure to transform a regular expression of size to an -free nondeterministic finite automaton yields automata with states and ( ) transitions. For a long time this was supposed to be also the lower bound, but a result by Hromkovic showed how to build an -free NFA with only ( log()) transitions. The current lower bound on the number of transitions is Ω( log()). A rough running time estimation for the common follow sets (CFS) construction proposed...

Algebraic and graph-theoretic properties of infinite -posets

Zoltán Ésik, Zoltán L. Németh (2010)

RAIRO - Theoretical Informatics and Applications

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A -labeled -poset is an (at most) countable set, labeled in the set , equipped with partial orders. The collection of all -labeled -posets is naturally equipped with binary product operations and -ary product operations. Moreover, the -ary product operations give rise to -power operations. We show that those -labeled -posets that can be generated from the singletons by the binary and -ary product operations form the free algebra on in a variety axiomatizable...

Random Generation for Finitely Ambiguous Context-free Languages

Alberto Bertoni, Massimiliano Goldwurm, Massimo Santini (2010)

RAIRO - Theoretical Informatics and Applications

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We prove that a word of length from a finitely ambiguous context-free language can be generated at random under uniform distribution in ( log ) time by a probabilistic random access machine assuming a logarithmic cost criterion. We also show that the same problem can be solved in polynomial time for every language accepted by a polynomial time -NAuxPDA with polynomially bounded ambiguity.

Finite repetition threshold for large alphabets

Golnaz Badkobeh, Maxime Crochemore, Michaël Rao (2014)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

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We investigate the finite repetition threshold for -letter alphabets, ≥ 4, that is the smallest number for which there exists an infinite -free word containing a finite number of -powers. We show that there exists an infinite Dejean word on a 4-letter alphabet (a word without factors of exponent more than 7/5 ) containing only two 7/5 -powers. For a 5-letter alphabet, we show that there exists an infinite Dejean word containing only 60 5/4 -powers, and we conjecture...